Long time lurker, first post. I used to throw almost exclusively forehand, but I'm trying build a dependable backhand drive. I've been trying to work on the right pec drill. How am I doing? What areas need work?

Welcome! Your foundation is off. Moving the right leg right by about 5-6" keeps you from bobbing up and down and swaying left and right from throw to throw if you also pivot on the heel or ball of the foot alone. Or start with heel moving weight forward on the ball of he foot and pivot there. The arm should swing on the same plane prior to disc separation and after it. Once you change these your accuracy ad consistency should improve. Then we could really see what's going on. Please post new videos after these changes so that you don't need to correct form oddities with other form oddities of different direction. You're better off learning good basics right away.

Flat shots need running on the center line of the tee and planting each step on the center line. Anhyzer needs running from rear right to front left with the plant step hitting the ground to the left of the line you're running on. Hyzer is the mirror of that.